#include<fstream.h>

long a[5000000], i, n, p, u, deque[5000000], k;
long long s;

int main()

{
	ifstream f("deque.in");
	ofstream g("deque.out");
	
	f>>n>>k;
	for (i=1;i<=n;i++) f>>a[i];
	
	deque[1]=1;u=1;p=1;s=0;
	for(i=2;i<=n;i++)
	{
		while (a[deque[u]]>=a[i] && u>p) u--;
		if (a[deque[u]]<a[i])u++;
		deque[u]=i;
		if (i-k==deque[p]) p++;
		if (i-k>-1) s+=a[deque[p]];
	}
	
	g<<s<<"\n";
	f.close();
	g.close();
}